1. Field of the Invention
This invention relates to oxidative conversion of organosulfur compounds in a mixture of hydrocarbons using liquid oxidants.
2. Description of Related Art
Desulfurization of petroleum fractions of light and heavy gas oil is typically carried out in the refinery through the catalytic hydrodesulfurization (HDS). However, it is known that HDS treatment is limited, in particular due to the fact that sterically hindered organic sulfur compounds are not reactive at mild HDS conditions (e.g., 30 Kg/cm2 of hydrogen partial pressure). The sulfur heteroatom in sterically hindered molecules, such as dibenzothiophene (DBT) derivatives including 4,6-dimethyldibenzothiophene (4,6-DMDBT), cannot be exposed to active catalytic sites in conventional HDS processes. Therefore aromatic rings in such sterically hindered sulfur molecule must first be hydrogenated, which requires high operating severity, in order to remove the steric hindrance surrounding the sulfur heteroatoms for catalytic HDS.
Oxidative desulfurization (ODS) is a known alternative or complementary process for deep desulfurization, and many ODS processes operate under relatively mild conditions and do not require use of hydrogen gas. In addition, ODS is efficient for desulfurization of organosulfur compounds such as DBT and its derivatives, particularly those characterized by one or more sterically hindered sulfur heteroatoms.
Typical ODS processes involve an oxidation step in which organic sulfur compounds are oxidized by a source of reactive oxygen. The oxidized organosulfur compounds are then removed or subject to further reaction to selectively remove the sulfur heteroatom. For instance, DBT and its derivatives are oxidized to produce DBT-sulfoxide and DBT-sulfone, which can be removed by known extraction and/or adsorption methods.
Known oxidants for ODS processes include liquid oxidants such as hydrogen peroxide or organic peroxides, or gaseous oxidant such as air or oxygen. However, certain process requirements and inefficiencies can pose operational or economic limitations to viable ODS operations.
In particular, transportation, handling and storage of liquid oxidants such as hydrogen peroxide and/or organic peroxides are potentially hazardous activities that require heightened safety precautions, and therefore impart significant expense in existing ODS processes.
Therefore, it would be desirable to provide an oxidative process for converting heteroatoms into their corresponding oxides that minimizes the need for transportation, handling and storage of hydrogen peroxide and/or organic peroxides.